Improving probes of hAA coupling in the Type-X two Higgs doublet model scenario: The crucial role of τ-jet charge identification

The exotic decay modes of the already discovered 125-GeV scalar into a pair of light pseudoscalars are a good probe of those new physics scenarios where such pseudoscalars exist. Searches in the mass region where the pseudoscalar (A) is lighter than 62.5 GeV have yielded null findings so far. No search has yet examined $m_A>62.5$ GeV where the cross section is suppressed by the off-shell pseudoscalar. We point out a possible enhancement of the sensitivity of probing hAA coupling in the context of a Type-X two Higgs doublet model. We focus on $h\to A{A}^{(⁎)}\to 4\tau$, and select events with two same-sign τ-jets along with a pair of same-sign leptons. This enables much more effective background elimination than in the erstwhile proposed channels. Taking two values of the ττA coupling into account, we obtain limits on the hAA coupling that can be probed at 2σ and 3σ significance, for $m_A$ ranging up to 85 GeV. For $m_A<62.5$ GeV, too, we find the probe through our suggested channel exhibits considerable improvement upon the usual $2\mu 2\tau$-based searches conducted at the LHC. Within this region, achieving the reach of ${\lambda }_{hAA}$ coupling at 3000 fb⁻¹ luminosity using our strategy would require approximately ∼ 3.6$\times {10}^5$ fb⁻¹ luminosity using conventional $2\mu 2\tau$-based searches.